Cutting of single-walled carbon nanotubes by ozonolysis

Cutting of single-walled carbon nanotubes (SWNT) has been achieved by extensive ozonolysis at room temperature. Perfluoropolyether (PFPE) was selected as a medium for cutting SWNT due to its high solubility for ozone (O3). A mixture of 9 wt % of O3 in O2 was bubbled through a homogeneous suspension of pristine SWNT in PFPE, at room temperature. The intense disorder mode in the Raman spectra of ozonated SWNT indicates that extensive reaction with the sidewalls of SWNT occurs during ozonolysis. Atomic force microscopy (AFM) images of SWNT, before and after ozonolysis, provided a measure of the extent of the cutting effects. Monitoring of the evolved gases for both pristine and purified SWNT indicates CO2 was produced during the ozonolysis process with a dependence on both system pressure and temperature. During heating, FTIR analysis of gases released indicated that carbon oxygen groups on the sidewalls of SWNT are released as CO2. SWNT was found to be extensively cut after an ozone treatment with a yield of approximately 80% of the original carbon.     

Environmental perchlorate: why it matters

The only known mechanism of toxicity for perchlorate is interference with iodide uptake at the sodium-iodide symporter (NIS). The NIS translocates iodide across basolateral membranes to the thyroid gland so it can be used to form thyroid hormones (TH). NIS is also expressed in the mammary gland during lactation, so that iodide can be transferred from a mother to her child. Without adequate iodide, an infant cannot produce sufficient TH to meet its developmental needs. Effects expected from perchlorate are those that would be seen in conditions of hypothyroidism or hypothyroxinemia. The probability of a permanent adverse effect is greatest during early life, as successful neurodevelopment is TH-dependent. Study of perchlorate risk is complicated by a number of factors including thyroid status of the mother during gestation, thyroid status of the fetus, maternal and infant iodine intake, and exposure of each to other TH-disrupting chemicals. Perhaps the greatest standing issue, and the issue most relevant to the field of analytical chemistry, is the simple fact that human exposure has not been quantified. This review will summarize perchlorate's potential to adversely affect neurodevelopment. Whether current environmental exposures to perchlorate contribute to neuro-impairment is unknown. Risks posed by perchlorate must be considered in conjunction with iodine intake.     

Fixed points of uniformly lipschitzian mappings

Two fixed point theorems for uniformly lipschitzian mappings in metric spaces, due respectively to E. Lifšic and to T.-C. Lim and H.-K. Xu, are compared within the framework of the so-called CAT(0) spaces. It is shown that both results apply in this setting, and that Lifšic’s theorem gives a sharper result. Also, a new property is introduced that yields a fixed point theorem for uniformly lipschitzian mappings in a class of hyperconvex spaces, a class which includes those possessing property (P)$\left(P\right)$ of Lim and Xu.     

Micromachined high frequency PMN-PT/epoxy 1-3 composite ultrasonic annular array

This paper reports the design, fabrication, and performance of miniature micromachined high frequency PMN-PT/epoxy 1-3 composite ultrasonic annular arrays. The PMN-PT single crystal 1-3 composites were made with micromachining techniques. The area of a single crystal pillar was 9 × 9 μm. The width of the kerf among pillars was ∼5 μm and the kerfs were filled with a polymer. The composite thickness was 25 μm. A six-element annular transducer of equal element area of 0.2 mm² with 16 μm kerf widths between annuli was produced. The aperture size the array transducer is about 1.5 mm in diameter. A novel electrical interconnection strategy for high density array elements was implemented. After the transducer was attached to the electric connection board and packaged, the array transducer was tested in a pulse/echo arrangement, whereby the center frequency, bandwidth, two-way insertion loss (IL), and cross talk between adjacent elements were measured for each annulus. The center frequency was 50 MHz and −6 dB bandwidth was 90%. The average insertion loss was 19.5 dB at 50 MHz and the crosstalk between adjacent elements was about −35 dB. The micromachining techniques described in this paper are promising for the fabrication of other types of high frequency transducers, e.g. 1D and 2D arrays.     

Talker-identification training using simulations of binaurally combined electric and acoustic hearing: generalization to speech and emotion recognition

Understanding speech in background noise, talker identification, and vocal emotion recognition are challenging for cochlear implant (CI) users due to poor spectral resolution and limited pitch cues with the CI. Recent studies have shown that bimodal CI users, that is, those CI users who wear a hearing aid (HA) in their non-implanted ear, receive benefit for understanding speech both in quiet and in noise. This study compared the efficacy of talker-identification training in two groups of young normal-hearing adults, listening to either acoustic simulations of unilateral CI or bimodal (CI+HA) hearing. Training resulted in improved identification of talkers for both groups with better overall performance for simulated bimodal hearing. Generalization of learning to sentence and emotion recognition also was assessed in both subject groups. Sentence recognition in quiet and in noise improved for both groups, no matter if the talkers had been heard during training or not. Generalization to improvements in emotion recognition for two unfamiliar talkers also was noted for both groups with the simulated bimodal-hearing group showing better overall emotion-recognition performance. Improvements in sentence recognition were retained a month after training in both groups. These results have potential implications for aural rehabilitation of conventional and bimodal CI users.     

Dynamical thermal effects in InGaAsP microtubes at telecom wavelengths

We report on the observation of a dynamical thermal effect in InGaAsP microtubes at telecom wavelengths. The microtubes are fabricated by releasing a strained semiconductor bilayer and are picked up by abruptly tapered optical fibers for subsequent coupling with adiabatically tapered optical fibers. As a result of absorption by InAs quantum dots embedded in the tube structure, these microtubes show dynamical thermal effects at wavelengths around 1525 nm and 1578 nm, while they are passive at longer wavelengths near 1634 nm. The photon absorption induced thermal effect is visualized by generating a pair of microbottles. The dynamical thermal effect can be avoided or exploited for passive or active applications by utilizing appropriate resonance wavelengths.     

Arsolyl-supported intermetallic dative bonding

The first examples of late transition metal η⁵-arsolyls (L = CO, P(OMe)₃; R = Ph, Me, Et, SiMe₃; R′ = Ph, H, Me, Et, Me) serve as ditopic donors to extraneous metal centres (M = Pt^II, Au^I, Hg^II) through both conventional As → M and polar-covalent (dative) Co → M interactions.

Cobalt carbonyl reacts with arsoles to provide the first late transition metal η⁵-arsolyls. These serve as ditopic donors to extraneous metal centres (M = Pt^II, Au^I, Hg^II) through both conventional AsM and polar-covalent (dative) CoM interactions.     

Spectroscopic Studies of Mononuclear Molybdenum Enzyme Centers

A concise review is provided of the contributions that various spectroscopic methods have made to our understanding of the physical and electronic structures of mononuclear molybdenum enzymes. Contributions to our understanding of the structure and function of each of the major families of these enzymes is considered, providing a perspective on how spectroscopy has impacted the field.     

ChemInform Abstract: Structure and Heats of Formation of Iodine Fluorides and the Respective Closed‐Shell Ions from CCSD(T) Electronic Structure Calculations and Reliable Prediction of the Steric Activity of the Free‐Valence Electron Pair in ClF6‐, BrF6‐, and IF6‐

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